The present invention relates to image registration systems for exposing photosensitive media, such as film, and, in particular, to a track mounted, spring biased registration pin system.
Imaging systems form a vital part of the printing industry and assure proper transfer of original master artwork to the printing plate, either directly or via an intermediate photosensitive media or film from which the printing plate is prepared. Critical to the process for multi-color printing is the necessity of maintaining the media in registration with the artwork through successive exposures to assure proper eventual alignment of the different color printings on the carrier media.
Three dimensional registration is required to assure the integrity of the exposed media. That is, the media and artwork must be longitudinally, laterally and vertically registered to a media support assembly. A common support assembly is known as a "vacuum frame". Vertical alignment can be achieved within the frame assembly with the use of various resilient pads, pressurized bladders or vacuum support assemblies, which maintain the media and artwork in flattened registration to a glass coverplate.
Longitudinal and lateral registration is commonly obtained with fixed height registration pins provided at the media support assembly. These pins may extend through holes in a resilient media support or may merely rest on the resilient support or an intermediate substrate. Such mountings can create difficulties in either mounting the media and artwork to the support or can produce a slight shifting or mis-registration of the media, due to the tipping of the pins during vacuum draw-down. Any mis-registration can become exaggerated over time with wear.
Various permanently mounted pin registration assemblies are disclosed in U.S. Pat. Nos. 4,636,067 and 4,967,230. The latter devices disclose media supports having individual bore holes through which individual registration pins extend. The pins of each of these assemblies rest on a relatively rigid backing piece which mounts below an overlying resilient layer.
A vacuum frame assembly is disclosed in U.S. Pat. No. 4,032,233 which provides grooved peripheral channels and along which a number of registration pins are moveably restrained. The pins are particularly coupled to a pinion containing, screw follower shaft which cooperates with pinions provided at each registration pin to simultaneously adjust each pin. The channelways surround the vacuum blanket, in contrast to being incorporated into the blanket. The pins thus restrain the periphery of the media and artwork, but which can induce a "cupping" and mis-register at the center region of the media during vacuum draw down.
The pins of each of the foregoing assemblies are also essentially permanently mounted. The pins cannot be independently replaced, re-positioned or varied in shape to mate with different hole configurations.
Support assemblies sold by the present assignee for use with vacuum frames of various manufacturers and which have proven effective are known under the brandname of IMAGE CONTROL BOARDS. These boards provide a resilient, yet rigid underlayment that contains a number of permanently mounted registration pins. The boards mount between a glass cover and vacuum blanket at the vacuum frame assembly.
Applicant, otherwise, believes it is preferable to register the media and artwork along a single edge and at a center portion of the media as opposed to the peripheral edges. The media and artwork are thereby able to flex and self adjust to the transparent cover as a vacuum is drawn. Ripples and other misalignment which can occur and/or tipping of the registration pins is thereby minimized.
With the foregoing in mind, applicant has developed an improved registration pin support assembly. The assembly is alternatively applied in one vacuum frame construction wherein an inflatable vacuum mat is formed to include slide adjusted registration pins. Another construction provides a channeled, non-inflatable mat which is constructed to permit use with existing vacuum frames.